Ryanodine receptors (RyRs) are intracellular channels that release calcium ions from the sarcoplasmic reticulum (SR) in response to either plasma membrane depolarization (in skeletal muscle) or increases in the concentration of intracellular free Ca2+ (in the heart). A gene (beta 4) encoding a ryanodine receptor (similar to, but distinct from, the muscle RyRs) was identified. The beta 4 gene was expressed in all tissues investigated, with the exception of heart. Treatment of mink lung epithelial cells (Mv1Lu) with transforming growth factor beta (TGF-beta) induced expression of the beta 4 gene together with the release of Ca2+ in response to ryanodine (but not in response to caffeine, the other drug active on muscle RyRs). This ryanodine receptor may be important in the regulation of intracellular Ca2+ homeostasis.